Method for fabricating an electron discharge device



1966 v. c. CAMPBELL ETAL 3,

METHOD FOR FABRICATING AN ELECTRON DISCHARGE DEVICE Filed Oct. 5, 1963 2Sheets-Sheet 1 O U N U 1. R P 0 w m M R S m C A F V K D m c N N w M U vF W E on v ""fl 231 mm 2339; mag/E62 m 9 37 02:5: p U C.UDOZ m a n d 7 w2 a m M BY THEIR ATTORNEY.

Dec. 13, 1966 v. c. CAMPBELL ETAL 3,291,549

METHOD FOR FABRICATING AN ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 2Filed Oct.

lN-VENTORSZ VON c. CAMPBELL,

FRANK A. ROMANO,

EDMUND F. SCHILLING,

TRIGGER PULSE SOURCE THEIR ATTORNEY.

United States Patent ()fifice Patented Dec. 13, 1966 This inventionrelates to a method for fabricating an electron discharge device.

In one form of light valve apparatus, an electron discharge device isprovided having a writing chamber envelope member and an electron gunmember which is mounted and hermetically sealed to the envelope member.The gun member includes a plurality of elements of electricallyinsulative refractory material forming a chamber for the gun. Aplurality of gun electrodes and a suitable brazing filer material arepositioned between the refractory material elements. By heating the gunmember assembly to a temperature and for a period of time necessary tocause brazing between the elements and electrodes, a rigid hermeticallysealed gun member assembly is formed.

It is desirable to test various electrical characteristics of theassembled gun member such as cathode emission and the alignment of thevarious gun components prior to final assembly of the discharge device.To effect testing, it is necessary that the elements of the gun memberbe outgassed, the gun chamber be evacuated, and that a beam currentcollector electrode be provided. The brazing process to which the gunmember assembly is subjected advantageously lends itself to outgassingthe member since the temperature of the brazing process, in addition tocausing adhesion of the various elements, can be selected to be suitablyhigh for outgassing the various gun elements. Brazing the gun memberassembly in a vacuum chamber and mounting an electrically conductiveclosure element at an end of the gun member provides an evacuated andoutgassed electron gun capsule having a beam current collectorelectrode. The capsule thus formed is adapted for testing the electricalcharacteristics of the gun member prior to final assembly. A dischargedevice having these features is disclosed in copending applicationSerial No. 313,693, filed October 3, 1963 and assigned to the assigneeof the present invention.

Subsequent to the electrical testing of the gun member and prior tomounting the member to the writing chamber envelope, an aperture isformed in the electrically conductive closure end element in order toprovide an unobstructed passage for an electron beam from a sourcewithin the gun member to the writing chamber of the discharge device.Formation of this aperture can conventionally be accomplished bymachining. Formation of the aperture exposes the interior of the gunmember to atmospheric pressure thus requiring that the gun member bere-evacuated and that the components be re-outgassed prior to use. Thegun member is mounted and hermetically sealed to the envelope member andfinal evacuation and outgassing of the assembled device is thenaccomplished.

Final outgassing and evacuation is generally performed in foursequential pumping phases. A vacuum pump which is coupled to theenvelope member initially evacuatcs the device to a desired reducedpressure. During a second phase and while the envelope is being pumped,various components which are mounted within the writing chamber areheated by RF induction currents. Outgassed products of this phase areremoved by pumping until a desired reduced pressure is again attained.The electrodes of the gun member are heated by RF induction currentsduring a third phase and the outgassed products are similarly removed bypumping. The cathode electrode is heated and outgassed as the productsare removed by pumping. Finally a chamber separating disk is heated byelectron bombardment. Pumping continues until the desired finaloperating pressure is attained within the envelope.

The above described processing of the discharge device is inefiicient inthat duplicate outgassing and evacuation of the gun member is requiredand the processing time for the discharge device is consequentlyextended. Furthermore, outgassing of the aperature disk by electronbombardment requires substantially more time than is required when thedisk was initially heated and outgassed.

.It can require as much as three to four hours in order to complete thedescribed outgassing-evacuation cycling. When it is desirable to producelarge quantities of the electron discharge device at economical cost,this lengthy processing time is disadvantageous.

Accordingly, it is an object of this invention to provide an improvedmethod for processing an electron discharge device.

Another object of this invention is to provide a method of outgassingand evacuation of an electron discharge device which can be accomplishedin a relatively short time.

Another object of this invention is to provide a method of outgassingand evacuation for a discharge device of the type referred to which isrelatively less costly than known methods.

A further object of the present invention is to provide a method ofoutgassing and evacuation for a discharge device whereby an electron gunmember is outgassed and evacuated independently and re-outgassing andre-evacuation is thereby avoided.

In accordance with the present invention, an electron gun memberassembly having aclosure end member is brazed in an evacuated atmosphereat a temperature suitable for both brazing the assembly and foroutgassing the various elements of the electron gun. The electron gunmember is mounted and hermetically sealed to a writing chamber envelopemember of an electron discharge device. Various components in thewriting chamber are heated to an outgassing temperature while thewriting chamber is simultaneously vacuum pumped to a desired operatingpressure and then tipped ofil. A focused coherent light beam which isderived from a source external to the device is projected through atransparent segment of the device upon a surface of the processing endmember to form an aperture therein and to provide an unobstructedelectron beam passageway from the gun member to the writing chamber.

By this process, the various elements of the electron gun areadvantageously outgassed during the brazing operation and the gun memberis evacuated and hermetically sealed. The additional step ofre-outgassing the gun member is eliminated; the gun chamber can beprocessed independently; and the time and cost in processing theelectron discharge device is materially reduced.

These and further objects, features and the attending advantages of theinvention will be apparent with reference to the following specificationand drawings in which:

FIGURE 1 is a view of a discharge device of the type essing end element22.

referred to and illustrates a step in the fabrication process of thepresent invention;

FIGURE 2 is a perspective view of an electron gun member for an electrondischarge device of the type utilized in a light valve projectionapparatus;

FIGURE 3 is a sectional view of the electron gun member of FIGURE 2taken along lines 3-3 of FIGURE 2;

FIGURE 4 is an enlarged partial view of the device of FIGURE 1illustrating the mounting of an electron gunmember to an envelopemember;

FIGURE 5 is a view taken along lines 55 of FIG- URE l, and

FIGURE 6 is a diagram illustrating in greater detail a coherent lightgenerator shown in FIGURE 1.

Referring now to the drawings, a electron discharge device 10 of thetype previously referred to is illustrated in FIGURE 1. The dischargedevice includes both an envelope member 12 forming a writing chamber andan electron gun member 14 for generating an electron beam. It isdesirable to assemble the gun member 14 and to test various electricalcharacteristics of the member. prior to mounting and hermeticallysealing it to the envelope member.

The gun member 14 is shown in greater detail in FIG- URE 2 and 3. Themember includes a body element 16, a base element 18, a spacer element20, and a proc- Segments 24 and 26 of gun electrodes 28 and 30 aresandwiched between the housing elements 18 and 16 and between 16 andrespectively. They are secured in position by a brazing filler material19 which forms a hermetic seal at these joints when the gun memberassembly is heated to a brazing temperature. End element 22 is securedto spacer element 20 by brazing filler material 19 which forms ahermetic seal at this joint. A more detailed description of the capsuleis given in the above referred to copending patent application.

The described assembly is jig mounted, positioned within a metalliccontainer in a vacuum chamber, and heated to the proper brazingtemperature. lthough various types of vacuum chambers are known, anillustrative example is a pressure sealed bell-jar having a vacuum pumpcoupled thereto. Evacuation of the chamber progresses until a suitablylow pressure is attained. A typical chamber pressure is 10- Torr.Heating means comprising an RF induction heating apparatus is provided.The induction apparatus may comprise an electrically exicted inductivecoil which is physically located within the vacuum chamber or it may bearranged external to the vacuum chamber in a manner for providing thatits generated field encompasses the container within which the gunassembly is positioned. The gun assembly which is heated primarily bythermal radiation from the container is raised to a temperature forcausing both brazing of the capsule and outgassing of the variouscomponents of the capsule. In one form of gun member as is described inthe above referred to copending application, a temperature suitably highfor providing brazing and outgassing is 1100 C. The electron gun memberat this stage of fabrication comprises an evacuated and hermeticallysealed capsule adapted for testing of certain electrical characteristicsas is discussed more fully in the referred to copending application.

Subsequent to testing, the sealed gun member 14 is mounted andhermetically sealed to the envelope member 12. A gun member supportelement 32 is hermetically sealed to the gun member as shown in FIGURE3. The gun member is then mounted and hermetically sealed to theenvelope by a conventional glass sealing technique such as flowing ahead of glass 36 from a neck portion 38 of the envelope about the edgeof support element 32. This mounting arrangement is best shown in FIG-URES 3 and 4.

A vacuum pump 39 is coupled to the envelope 12 through a tip-ofi tube40. The pump 39 evacuates the envelope 12 until a desired pressure isattained within the envelope. Various elements within the envelope suchas metallic support elements, not shown, for a disk 59 are heated by anRF induction heating apparatus 44. Apparatus 44 is of the type forgenerating an RF field and for directing and concentrating the field onvarious elements within the glass envelope l2. Outgassed products of theheated elements increase the pressure within the envelope 12. Theenvelope is continuously pumped until these products are substantiallyremoved, and a desired pressure is attained. Tip-oil is then effectedwhereby the pump 39 is detached and the device 10 is hermeticallysealed.

In order to provide an unrestricted passage for an electron beam fromthe gun member 14 to the Writing chamber of envelope 12, an aperture isnow formed in a surface of end processing element 22. A coherent lightbeam generator 46 is provided which generates a coherent light beam 47.The beam 47 is projected through a double concave lens 48; through atransparent output window 49 of the device 19; through a transparenttransport disk 50 at a point 51 which is bare of a conductive substrate52; and through an aperture 53 in a light shield 54; and onto thesurface of element 22. The lens 48 focuses the beam onto the surface 22and the concentrated energy of the impinging light beam causes thetemperature of the surface of element 22 to rise. Beam impingementcontinues for a period of time required to form an aperture in the endprocessing element 22.

In FIGURE 6, the generator 46 is shown in greater detail. The coherentlight source may comprise a laser having a synthetic ruby crystal rod 60which is doped with chromium. A helical shaped Xenon filled flash coil61 is positioned about the rod 60. One end of the rod has a depositedsilver surface 62 for providing substantially 100% reflection While anopposite end 63 is coated to provide substantially reflection. A triggerpulse voltage 6 is derived from a source 65 and stepped up in levelto-approximately 50 kv. by a transformer 66. A secondary winding of thetransformer is coupled to a trigger rod 67 which initiates discharge ofthe gas within coil 61. The greater portion of electrical energynecessary for sustaining the discharge for a desired interval is derivedfrom a capacitor 68 which has been charged from a D.C. power supply 69through a current limiting resistor 70. The operation of this type ofcoherent light beam generator is known. A more detailed description isgiven in Radio-Electronics, pages 28-32, January 1963.

Thus, a method for fabricating an electron discharge device is describedwhich simplifies the fabrication of a discharge device and eliminatesthe need for re-outgassing and re-evacuating a gun member andconsequently reduces the time and cost required for its construction.

While I have illustrated and described and have pointed out certainnovel features of my invention, it will be understood that variousomissions, substitutions, and changes in the forms and details of thesystem illustrated may be made by those skilled in the art withoutdeparting from the spirit of the invention and the scope of the claims.

What I claim is:

1. A method of fabricating an electron discharge device for a lightvalve apparatus including a forming operation which is accomplished bythe application of thermal energy to a body comprising: the steps ofmounting and hermetically sealing an electron gun member having aprocessing end element to an envelope for the device, said envelopehaving a transparent segment; pumping said device to provide adifference in pressure between the interior and exterior of theenvelope; and projecting a focused coherent light beam upon said endelement for a period of time for causing an aperture to be formedtherein. 7

2. A method of fabricating an electron discharge device of the typeincluding an envelope member having a transparent segment thereof and anelectron gun member 5 6 assembly having an end processing elementcomprising: time for causing the end processing element to heat to a thesteps of heating the gun member assembly in a temperature for forming anaperture therein.

vacuum chamber to a temperature for causing outgassing and brazing ofthe gun member components; mounting References Cited by the Exammer thegun member assembly to the envelope and providing 5 UNITED STATESPATENTS a hermetic seal therebetween; heating and vacuum pump- 2,474,3356/1949 Skellett 316 25 X ing the envelope member to a temperature foroutgassing 3,096,767 7/ 1963 Gresser et a1.

components of the envelope member and to a desired 3,210,171 10/ 1965MacDonald.

vacuum respectively; and projecting a focused coherent light beamthrough a transparent segment of said enve- 10 RICHARD EANES P'lmaryExammerlope and onto the end processing element for a period of FRANK E.BAILEY, Examiner.

1. A METHOD OF FABRICATING AN ELECTRON DISCHARGE DEVICE FOR A LIGHTVALVE APPARATUS INCLUDING A FORMING OPERATION WHICH IS ACCOMPLISHED BYTHE APPLICATION OF THERMAL ENERGY TO A BODY COMPRISING: THE STEPS OFMOUNTING AND HERMETICALLY SEALING AN ELECTRON GUN MEMBER HAVING APROCESSING AND ELEMENT TO AN ENVELOPE FOR THE DEVICE, SAID ENVELOPEHAVING A TRANSPARENT SEGMENT; PUMPING SAID DEVICE TO PROVIDE ADIFFERENCE IN PRESSURE BETWEEN THE INTERIOR AND EXTERIOR OF THEENVELOPE; AND PROJECTING A FOCUSED COHERENT LIGHT BEAM UPON SAID ENDELEMENT FOR